CN114069247A

CN114069247A - High-Gain 5G Antenna Lenses for Beam Convergence

Info

Publication number: CN114069247A
Application number: CN202111233178.7A
Authority: CN
Inventors: 高巨
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2021-10-22
Filing date: 2021-10-22
Publication date: 2022-02-18

Abstract

High-gain 5G antenna lenses that can achieve beam convergence belong to the field of 5G communications. The lens is discretized, and the layers are nested. The structure of each layer is a concentric cylindrical structure of 6 layers at the center of the circle; each layer is in a nested form. Hollow cylindrical structure, each layer is embedded in the hollow cavity of the outer layer. The dielectric constant of the lens decreases gradually from the inner layer to the outer layer. In this study, a compressed Lumberg lens is used as a dielectric radome, and the principle of optical change and discrete processing methods are used to improve the radiation gain of the original radiating antenna, reduce the lobe width, and improve the scanning sensitivity of the 5G antenna.

Description

High-gain 5G antenna lens capable of realizing wave beam convergence

The technical field is as follows:

the invention belongs to 5G communication, and relates to an electromagnetic field and an antenna.

Background art:

the 5G technology commercial system architecture is typically composed of a Core Network (CN), a baseband unit (BBU), and an Active Antenna Unit (AAU). The basic architecture is that a core network supports a plurality of baseband units, and each baseband unit will support a plurality of active antenna units. Due to the fact that the bandwidth reaches 400MHz and even is wider, a high sampling rate digital-to-analog converter (DAC) and an analog-to-digital converter (ADC), real-time processing of mass data and high-density integration of a large number of radio frequency channels and antennas are the bottleneck of 5G millimeter waves based on the massive MIMO technology. For this reason, the 5G millimeter wave active antenna elements currently commercialized adopt a hybrid multi-beam scheme of a phased sub-array. This approach greatly reduces the number of radio frequency transceivers, partially overcoming the bottleneck problem described above, but at the expense of array gain and communication capacity. This is also why current 5G systems fail to achieve the intended "everything interconnect" goal.

Aiming at the problems of insufficient gain and insufficient flexibility in beam width regulation in the current commercial 5G equipment, the existing solution is to utilize a mixed multi-beam framework and a common-caliber mixed multi-beam array. The advantage of the hybrid multi-beam architecture is that multi-beam coverage is accomplished with less complexity and cost. The system can realize the independent control of 4 beams only by adopting 4 ADC/DAC channels and up-down frequency conversion channels. However, since the 4 beams are independently controlled in a subarray fashion, this architecture does not achieve efficient use of the full aperture of the antenna, and thus 6dB (4 subarrays) or more of the array beam gain is lost.

Another more effective hybrid multi-beam architecture is to utilize both the beam forming of the baseband digital part and the analog beam forming of the phased sub-array to achieve the utilization of the full aperture of the antenna array and to generate higher array beam gain. However, because the beam width of the phased sub-array is limited, the multi-beam scanning range is narrowed, and the coverage range is limited. This architecture can achieve coverage extension through beam switching, but at the expense of delay and increased complexity of beam management, it will eventually result in system capacity reduction.

The invention content is as follows:

according to the research, the compressed luneberg lens is used as the dielectric radome, on the premise that the existing commercial laying equipment is not changed, the system gain is improved, the beam width is freely regulated and controlled, the beam scanning angle of the antenna array is increased, the beam scanning accuracy is improved, and the purpose of interconnecting everything is finally achieved.

For the new generation communication system, the relative advantages of the communication scheme at 60GHz are obvious. As frequencies increase, the design requirements and manufacturing standards for receive and transmit antennas in communication systems at 60GHz also increase. Not only is miniaturization of antenna design required, but also channel capacity, antenna gain, directivity, and radiation efficiency are considered. Although the designs of frequency selective surface, electromagnetic band gap shield, partial reflection surface and phase control jump are continuously optimized in the application of high-directivity antenna, and attempts are made to compensate the phase difference problem caused by different radiation path lengths by these methods, these designs still do not have the capability of taking into account frequency bandwidth, side lobe level or beam scanning.

In contrast, the above problems can be solved well by using the characteristics of the luneberg lens. Particularly, for the research on the compression of the Luneberg lens, on the basis of keeping the functions of the traditional Luneberg lens, the problem that the traditional Luneberg lens is large in size and limited in application in some practical occasions is solved, the size of the Luneberg lens can be greatly compressed in the incident wave direction, and the applicability of the Luneberg lens is greatly improved.

The traditional luneberg lens is compressed by utilizing an optical transformation theory, a layering processing manufacturing method is adopted, and the incident electromagnetic waves are weighted by utilizing the coupling effect between lenses on different layers after layering. The beam scanning capability of the compressed luneberg lens was studied by varying the relative positional displacement of the radiator and lens.

The traditional luneberg lens is a structure with a three-dimensional isotropic dielectric constant gradually changing, and can converge plane electromagnetic waves to a focus of the plane electromagnetic waves or convert spherical waves emitted by a point source placed at the focus into plane waves. The relative dielectric constant epsilon and the refractive index n of the internal space ordered arrangement of the luneberg lens and the position r of the luneberg lens in the lens range accord with the following formula:

here is that

A given point, i.e. the point to be investigated (assuming the problem under investigation is a plane in the yz plane). R is the radius of the entire lens. It is assumed here that the entire lens is a non-magnetic medium, i.e. μ ═ 1. Since the change of the relative permittivity of the luneberg lens from the surface to the center does not jump and the value of the relative permittivity at the surface is 1, which is the same as that of air, there is no reflection when the electromagnetic wave is incident from air to the luneberg lens.

When a point source is placed at the focus of the spherical luneberg lens, the electromagnetic waves are converted into plane waves after passing through the luneberg lens. For this reason, since the surfaces of the spherical lenses are all focal points, the spherical lenses can be used to detect the incoming wave direction. When plane waves are incident on the luneberg lens, electromagnetic waves are converged to a focus corresponding to the incoming wave direction through the luneberg lens, so that the incoming wave direction can be detected through the circle center and the focus, and the working principle and the main application of the luneberg lens are realized.

Since the luneberg lens sphere is bulky, its application in antennas, especially moving the antenna along the luneberg lens sphere surface, is very difficult. Therefore, it is proposed to transform the luneberg lens by using the optical transformation principle, while keeping most of the characteristics of the conventional luneberg lens, greatly compressing its volume.

Each layer is converted into a planar disc type according to a conventional luneberg lens formula, thereby facilitating processing. For ease of understanding, the refractive index of a conventional luneberg lens is understood as a function about the coordinate axis xy. The conventional luneberg lens is transformed by equation (2) to obtain a set of coordinates based on the compression factor δ:

y'＝y

where R is the outer radius of a conventional luneberg lens and δ is the compressibility, taken here as an arbitrary integer. Since maxwell's equations are invariant, the transformation to coordinates is equivalent to normalizing the constitutive parameters, fields and sources. Therefore, the relationship between the tensor values of the new permittivity and permeability and the transformed conventional luneberg lens can be expressed by the following formula:

and

here, the coefficients a and B can be expressed by equation (5) and equation (6):

this optical transformation formula does not change the working properties of the luneberg lens but only its shape. The medium obtained by the formula (3) utilizes a distorted virtual electromagnetic space to simulate passing through a medium with a higher refractive index, so that electromagnetic waves are rapidly converged. The inhomogeneous anisotropic material is required because the dielectric constant tensor is non-diagonal due to the non-conformality of the proposed transformation. By giving the compression factor, the relative permittivity distribution of different positions in the corresponding compressed luneberg lens can be obtained. The incorporated compressibility in this study was 7.

When the radiation source is placed on the spherical surface of the traditional luneberg lens, namely on the focal point, the electromagnetic wave passes through the luneberg lens and can be well converted into plane wave by utilizing the phase delay of the spherical wave in the spherical lens. If one wants to keep the focus on the compressed surface of the luneberg lens, it is necessary that the outer edge of the lens is approximately 13 wavelengths to obtain sufficient phase accumulation. Although the dimension in the z direction is reduced to a great extent, it is meaningless for practical application if the former dimension is maintained in the xy direction. It is desirable that the outer edge of the lens be comparable to the wavelength in order to be more practical.

The compressed luneberg lens subjected to optical transformation is discretized in view of simplification of the process. Each layer of the discretized lens is small compared with the wavelength, so that the electromagnetic waves are ensured to pass through each layer with small reflectivity, multiple reflection inside the lens is avoided, and the transmissivity and the working efficiency of the lens are improved.

The lenses are discretized and are sleeved layer by layer, and each layer of structure is in a 6-layer concentric cylinder structure at the circle center. The dimensions of the layers are shown in table 1. The parameters of the respective layer structures in table 1 were selected by calculation based on the relative relationship between the relative dielectric constant (epsilon) and the lens internal position (xy) in formula (3), and the continuous lens was discretized into a layered structure. Taking the dielectric constant of 12 to 10 as one layer, taking 10 to 8 as one layer, and so on. Finally, a 6-layer structure is obtained. Since the dielectric constant variation is non-linear, the thickness of each layer is not uniform after the dielectric constant of each layer is uniformly distributed. Each layer of the structure is in a nested form, except that the innermost layer is in a solid disc structure, the rest 2 to 6 layers are in hollow cylindrical structures, and each layer is just embedded into the hollow cavity of the other layer. The dielectric constant of the lens is gradually reduced from the inner layer to the outer layer and is 12,10,8,6,4,2, so that the convergence of the beams and the matching of the impedance with the air are ensured. A schematic structural diagram and a sample object are shown in figure 1.

TABLE 1 disc type compressed Luneberg lens layer size

The system radiation source adopts a 1-by-4 antenna array to simulate the existing commercial 5G antenna equipment, and a lens is arranged in front of the radiation opening surface of the antenna, so that a weighted regulation beam can be obtained. Comparing the weighted beam with the original array radiation beam, the gain addition capability and beam plasticity capability of the lens can be obtained. The simulation results of the radiation characteristics of the antenna array are shown in fig. 2.

The radiation source adopts a 1-4 linear array antenna array, and the vibration element adopts a horn antenna. From the results, it can be seen that the gain of the radiation source is 13.8dB, the E-plane lobe width is 19 °, and the H-plane lobe width is 69.4 °. The radiation pattern after the addition of the lens is shown in figure 3.

Through further optimization of the dielectric constant, the number of layers and the feed source position of the lens, the lens parameters with better beam convergence effect are obtained. Simulation results show that after the lens is optimized, the beam width of the E surface is 15.4 degrees, the beam width of the H surface is 12.9 degrees, and the gain is improved to 20.9 dB. The improvement in the performance of the loading lens on the radiation pattern is shown in table 2.

TABLE 2 improved contrast of lenses to radiation performance

Comparison of simulation results	Lens-free	With lenses	Contrast with or without lens
				Gain of	13.8dB	20.9dB	7.1dB improvement
Width of E-surface lobe	19°	15.4°	By reducing by 3.6 °
				Width of H-plane lobe	69.4°	12.9°	Reduce 56.5 degree

The effect of the loading lens on the radiation characteristic of the oscillator element can be seen visually in table 2. The improvement of the gain can greatly improve the communication distance between the 5G base station and the terminal and reduce the base station laying density; the reduction of the width of the radiation lobe can realize the convergence of the wave beam and improve the accuracy of the wave beam scanning of the 5G antenna.

Drawings

FIG. 1 is a schematic view of a compressed Luneberg lens

FIGS. 2(a) and (b) are the E-plane and H-plane radiation patterns, respectively, of a radiation source

FIGS. 3(a) and (b) are E-plane and H-plane radiation patterns, respectively, after loading the lens

The specific implementation mode is as follows:

the lens can be processed by 3D printing, the dielectric constant of the structure is gradually reduced from inside to outside, the dielectric constant of the innermost layer is 20, and the dielectric constant of the outermost layer is 2. By placing the radiation source in the focal plane of the lens, beam focusing and gain enhancement characteristics are achieved.

Key technology for manufacturing lenses:

1. the compression factor is 7.

2. The outer edge of the lens is approximately 13 times the wavelength

3. After calculating the dielectric constant distribution of the compression lens by the formula 3, the dielectric constants of the layers are averaged to obtain the size and the dielectric constant of each layer, and the specific requirements in the research are shown in table 1.

4. The structural layers are in a nested form.

5. The radiation source is placed in the focal plane of the lens, which in this study is at a distance of 62mm from the radiation source.

The advancement of the technology:

according to the research, the compressed luneberg lens is used as a dielectric radome, and the radiation gain of the original radiation antenna is improved, the lobe width is reduced, and the scanning sensitivity of the 5G antenna is improved by using an optical change principle and a discrete processing method. The dielectric lens designed by the technology has the following characteristics:

(1) the gain of the communication system can be improved. By utilizing the beam weighting and optical transformation principle, a compressed Luneberg lens is constructed, and the gain amplification of any radiation source can be realized.

(2) The beam scanning sensitivity is improved. The problem of insensitivity of the existing beam scanning is caused by the fact that the angle of the beam radiated by the antenna is too wide. The technology can well compress the radiation wave beam and improve the accuracy of the transmission link and the communication distance.

(3) The beam scanning range can be increased. The method has no conflict with the wave beam scanning range of the phased array antenna, and the compressed luneberg lens can provide secondary addition for wave beam scanning, namely, the wave beam scanning range is improved in a similar refraction mode on the basis of the original phased array wave beam scanning range.

(4) The integration is convenient. The non-resonance externally-hung structure adopted by the design can be conveniently loaded on the existing 5G base station and equipment, and the existing antenna does not need to be disassembled and assembled. In addition, when 6G communication is developed later, the lens designed by the inventor can also be applied to 6G frequency bands such as terahertz.

(5) And the cost control is facilitated. The 5G antenna loaded with the lens can radiate farther, and the coverage area under a single day is large, so that the laying density of the antenna base station can be reduced, and the cost is saved.

Claims

1. A high-gain 5G antenna lens that can realize beam convergence is characterized in that: the lens is discretized, and the layers are interlocked, and each layer structure is presented as a 6-layer concentric cylindrical structure at the center of the circle; each layer is a nested form, except The innermost layer is a solid wafer structure, and the remaining 2 to 6 layers are hollow cylindrical structures, each of which is just embedded in the hollow cavity of the outer layer; the dielectric constant of the lens gradually decreases from the inner layer to the outer layer.

2 . The high-gain 5G antenna lens capable of beam convergence according to claim 1 , wherein the outer diameter of the lens is 13 times the wavelength of the incident wave. 3 .

3 . The high-gain 5G antenna lens capable of beam convergence according to claim 1 , wherein the lens compression factor is 7. 4 .

4. The high-gain 5G antenna lens that can realize beam convergence according to claim 1, wherein:

The size and dielectric constant of each layer are obtained from the dielectric constant of each layer. The specific requirements are as follows:

.

5. The high-gain 5G antenna lens that can realize beam convergence according to claim 1, wherein the radiation source is placed on the focal plane of the lens.